The invention relates to an electrical connection between a potentiometer for detecting the actual position of an actuating element, a motor for operating the actuating element, and control electronics for controlling the nominal/actual value correction.
Such an electrical connection is required, for example, in so-called E-gas systems in motor vehicles. The potentiometer is in this case coupled to the engine throttle valve shaft, which can be rotated by operation of the actuating motor. The control electronics in this case compare the nominal value of the throttle valve position, governed by the gas pedal position, with the actual value determined by the potentiometer and, if necessary, carries out corrective measures by driving the actuating motor. The electrical components of the control loop have until now been connected to one another via cables, thus necessitating a large number of contact points. Apart from rigid links produced, for example, by welding or soldering, the contact points comprise connections or plug connections produced by crimping. The risk of contact problems increases with each additional contact point, however, irrespective of the design configuration. In the case of rigid connections, there is a risk of these connections being destroyed over a period of time as a result of the materials which are connected to one another having different thermal coefficients of expansion, in the event of temperature fluctuations, such as those which occur to a significant extent in the engine compartment of a motor vehicle. In the case of other types of connection, problems occur due to oxidation of the contact surfaces, or the contact resistances between the contact surfaces are very high owing to mechanical prestressing of the two contact partners being too low from the start or decreasing during use. It is also necessary to take account of the fact that the current carrying capacity of such connections is reduced under the influence of high temperatures (derating curve).
The production of contact points also requires a large number of processes, some of which can be automated only with difficulty and each of which intrinsically involves the risk of a process fault. A further disadvantage of mechanical connections is that the cables, plug sockets and plug housings represent components which are sensitive to vibration and which can become loose over a period of time, particularly with the vibration which is always present in the engine region of motor vehicles.
The object of the invention is to avoid the contact points required for an electrical connection of the type mentioned above, and thus to improve the reliability and to reduce the manufacturing costs.
According to the invention, the object is achieved by an electrical connection of the introduction mentioned type in which the base substrate of the potentiometer and the contact board of the motor are in the form of an integral board, and at least some of the electrical connections comprise conductor tracks embedded in the substrate.
This allows a large number of contact points to be avoided. The risk of faults during the production of the electrical connection is reduced by the conductor tracks embedded in the substrate. The electrical connection according to the invention has also been found to be highly resistant to vibration and temperature fluctuations. For example, the motor and the potentiometer can be connected to the control electronics via a single plug connection on the board. This avoids separate wiring for the potentiometer and motor.
In a further refinement, the invention provides for at least some of the electrical components of the control loop which comprises the potentiometer, motor and control electronics to be integrated on the board.
For example, inductors, brush braided-wire contacts and printed discharge resistors can be provided in the region of the motor. The potentiometer tracks are also preferably applied directly to the board by printing, and are connected to the embedded conductor tracks. These measures allow the previously required numbers of contact points to be reduced further.
In addition to a contact point for connection of the control electronics, further connecting points can be provided for motor contact tabs. As an alternative to the motor contact point, it is possible to design the board to have brush guide channels directly in the region of the motor.
In a preferred development of the invention, openings are provided at the contact points, into which openings the conductor tracks project elastically in the form of tongues from at least two opposite sides, with the distance between the ends of the contact tongues being less than the diameter or the width of the contact pin to be inserted or of the contact tab to be inserted.
Despite the simple insertion of the pins or contact tabs, this type of contact leads to a very good electrical connection, since the elastic tongues are first of all bent elastically by the contact pins, and their edges then subsequently make resilient contact with the surface of the contact pin. The very high surface pressure that results in this way ensures that a good electrical contact is made, with a low contact resistance. Since any tension applied to the contact pin increases the contact force between the conductor track tongues and the pin surface, such a connection at the same time forms reliable protection against the plug becoming loose due to vibration. On the other hand, material expansion resulting from different thermal influences does not lead to the connection being destroyed, since the contact tongues of the conductor tracks have a certain elasticity.
Since the conductor tracks are subject to different requirements in the different regions of the board, a further preferred embodiment of the invention provides for the conductor tracks to be composed of different materials in their individual regions. Thus, in the region of the already described contact point, the conductor track may be composed of a resilient material which ensures long-term elastic contact with the inserted contact pin.
The board may have a weak point between the motor region and the potentiometer region, with the conductor tracks which connect the two parts being exposed and flexible in the region of the weak point.
The embodiment with the weak point allows the motor board to be loosened before the rest of the board is actually fitted, thus allowing better matching to the physical characteristics. The electrical connection between the two board parts is not affected by this. Apart from compensating for tolerances, the motor can also be arranged inclined with respect to the potentiometer, or at right angles to it, in which case, however, it is necessary to ensure that the exposed conductor tracks can be deformed sufficiently.